Speed traps set up by unscrupulous law enforcement personnel have always been the bane of law abiding motorists. Because of this, radar detectors have been developed and are now in widespread use but these are expensive to purchase, quite often become outdated in a short time, and can be a source of harassment from local officials even though they are legal to use.
Basically, radar is an electronic system for determing the direction and range of anything that will reflect microwave radio signals. Traffic control radar is a microwave signal beamed toward the vehicle being monitored with such waves being reflected back to the radar unit. The unit then interprets the changing frequency of the microwaves received from the approaching vehicle, and based upon the time difference in the returning microwave, computes the speed of the vehicle according to such frequency change.